482 THE DESCENT OF MAN. 



have acted in a direct manner on the plumage; this may -have 

 had some effect, but I have not much confidence in so great a 

 difference as we sometimes see between the two plumages having 

 been thus caused. A more probable explanation Is, that an an- 

 cient style of plumage, partially modified, through the transfer- 

 ence of some characters from the summer plumage, has been 

 retained by the adults during the winter. Finally, all the cases 

 in our present class apparently depend on characters acquired by 

 the adult males, having been variously limited in their transmis- 

 sion according to age, season, and sex; but it would not be worth 

 while to attempt to follow out these complex relations. 



Class VI. The young in their first plumage differ from each 

 other according to sex; the young males resembling more or less 

 closely the adult males, and the young females more or less closely 

 the adult females. — The cases in the present class, though occur- 

 ring in various groups, are not numerous; yet it seems the most 

 natural thing that the young should at first somewhat resemble 

 the adults of the same sex, and gradually become more and more 

 like them. The adult male blackcap (Sylvia atricapilla) has a 

 black head, that of the female being reddish-brown; and I am 

 informed by Mr. Blyth, that the young of both sexes can be dis- 

 tinguished by this character even as nestlings. In the family of 

 thrushes an unusual niimber of similar cases have been noticed; 

 thus, the male blackbird (Turdus merula) can be distinguished 

 in the nest from the female. The two sexes of the mocking bird 

 (Turdus polyglottus, Linn.) differ very little from each other, yet 

 the males can eajsily be distinguished at a very early age from the 

 females by showing more pure white.^" The males of a forest- 

 thrush and of a rock-thrush (Orocetes erythrogastra and Petro- 

 cincla cyanea) have much of their plumage of a fine blue, whilst 

 the females are brown; and the nestling males of both species 

 have their main wing and tail-feathers edged with blue, whilst 

 those of the female are edged with brown." In the young black- 

 bird the wing feathers assume their mature character and be- 

 come black after the others; on the other hand, in the two spe- 

 cies just named the wing-feathers become blue before the others. 

 The most probable view With reference to the cases in the present 

 class is that the males, differently from what occurs in Class I., 

 have transmitted their colors to their male offspring at an earlier 

 age than that at which they were first acquired; for, if the males 



*" Audubon, 'Ornith. Biography," vol. i. p. 113. 



■" Mr. C. A. Wright, in 'Ibis,' vol. vi. 1864, p, 65. Jerdon, 'Birds of 

 India,' vol. i. p. 615. See also on the blackbird, Blyth in Cliarlea- 

 worth's 'Mag. of Nat. History,' vol. i. 1837, p. 113. 



